Nitrofurantoin is an antimicrobial agent used to treat urinary tract infections. However, systemic toxicities limit its usefulness. Our long term goal is to identify strategies which could be used to prevent, alleviate or reverse these toxic effects. Our working hypothesis is that tissue levels of glutathione and/or alpha-tocopherol are depleted during metabolic activation of nitrofurantoin leaving protein thiols, lipids and/or biomacromolecules vulnerable to attack by reactive oxygen species and drug metabolites. This leads to a disturbance of Ca2+ homeostasis, activation of nonlysosomal proteases and endonucleases, and cell death. We suggest that by studying both the toxicokinetics and toxicodynamics of nitrofurantoin in the isolated perfused rat liver, kidney and lung we will be able to determine the time sequence of the events which lead to irreversible injury. Then, by successively blocking or reversing each of these processes we will be able to establish effective strategies for lessening or preventing nitrofurantoin-induced toxicities. We have chosen probes which will inhibit the metabolism of the 5-nitrofurans (2'-AMP and allopurinol) or glutathione (penicillamine). We will replenish GSH (cysteine, glycine and glutamic acid) and vitamin E (alpha-tocopherol succinate). We will also scavenge reactive oxygen species (dimethylthiourea, AD-5), regenerate protein thiols (dithiothreitol) and inhibit Ca2+-activated nonlysosomal proteases (leupeptin). We will also use nifedipine, a Ca2+ channel blocker, to prevent the early influx of Ca2+. Further, we vary the concentration of Ca2+ in the perfusate. We will quantitate, as an indicator of oxidative stress, the time course of GSSG efflux into the perfusate and/or the bile. We will also measure tissue levels of GSH, GSSG and Vitamin E. We will monitor lipid peroxidation and oxidation of protein thiols. We will quantitate covalent binding to proteins, particularly in the plasma membrane; assess DNA fragmentation and chromatin condensation; and monitor proteolysis. We will quantitate intracellular Ca2+ concentrations using nuclear magnetic resonance. Organ damage will be assessed by using organ specific indices, by the appearance of lactate dehydrogenase in the perfusate and by gross and microscopic examination of the tissue. We have a unique opportunity to study nitrofurantoin in two organs for which it is toxic -- liver and lung -- and one in which it is not toxic -- the kidney. Thus, we will be able to compare the disposition of nitrofurantoin by each of these organs and the specific response of each of these organs whether or not manifest toxicity occurs. Our studies will also suggest appropriate therapeutic organs whether or not manifest toxicity occurs. Our studies will also suggest appropriate therapeutic interventions which may prevent or mitigate these toxicities without compromising its antimicrobial activity. As a consequence, new uses for nitrofurantoin and other 5-nitrofuran antimicrobials may be possible. For example, they are potent radiosensitizers in vitro, but at the doses needed in vivo side effects limit their usefulness. In addition, they have broad spectrum antibacterial and antifungal properties and might be used to treat the opportunistic infections that accompany AIDS and other immune deficiency diseases.